Electroplating anode structure



Feb. 19, 1957 E. v. BERRY 2,782,159

ELECTROPLATING ANODE STRUCTURE Filed June 29, 1953 5 Sheets-Sheet l Feb.19, 1957 E. v. BERRY 2,782,159

ELECTROPLATING ANODE STRUCTURE Filed June 29, 1953 5 Shets-Sheet 2 Feb.19, 1957 E. v. BERRY ELECTROPLATING ANODE STRUCTURE 5 Shets-Sheet 5Filed June 29, 1955 2,782,159 ELECTROPLATING ANODE STRUCTURE Ernest V.Berry, Los Angeles, Calif.

Application June 29, 1953, Serial No. 364,569 9 Claims. (Cl. 204-212) Myinvention relates to the field of electroplating, and more specificallyto an anode structure and method of us ng same particularly effective inchromium plating crank pins and main journals of crankshafts, as well asi tlher cylindrical surfaces such as calender rolls, and the Thepreviously available apparatus and methods. for electroplatingcylindrical surfaces with a layer of hard chromium have been foundunsatisfactory in that it is entremely ditficult to deposit a layerthereof of uniform thickness and proper homogeneous hardness, brightnessand density. The difficulties encountered in obtaining the desiredresults with previously available apparatus and methods stem from thefact that the electro-chernical reactions involved in chromiumelectroplating are not clearly understood. As a result, improvements inboth the apparatus and methods employed must be made from an empiricalapproach, rather than from a theoretical standpoint.

In contrast to plating with most other metals, commercial chromiumelectroplating is not carried out in a bath that is anaqueous solutionof one of its salts, but instead an electrolyte is employed that is awater solution of chromic and sulphuric acids. In addition, aninsolubleanode is utilized in this chromic acid bath.

The chromium in a chromic acid bath is initially in the hexavalentstate, but has a tendency to be reduced to the trivalent state duringthe plating operation. It is most important to hold the trivalentchromium content of the plating bath to a minimum in order to attainchromium plating of uniform physical characteristics.

' In the past, the chromium plating of main journal and crank pins ofcrankshafts has been accomplished by rotating the crankshaft in achromic acid bath in which the crankshaft serves as a cathode.Arcuately-shaped 'anode plates are then disposed adjacent thecylindrical "surfaces to be platted, with the cathode and anode con-]nected to a suitable source of direct electrical power.

From experience it has been found that this method of chromium platingis unsatisfactory as it is virtually impossible to deposit a chromiumlayer of uniform thickne'ss on a cylindrical surface thereby.

By trial and error it has been found thattthe plating characteristics ofa chromic acid bath are most sensitive to changes in the temperaturethereof, the current densities on the anode and cathode, the pH of thebath, and the chromic and sulphuric acid content thereof. For instance,an increase in the concentration of chromic acid in the bath increasesthe conductivity thereof, but at the sametime, decreases the cathodeefficiency so that in many cases a higher current density does. notincrease the rate of chromium deposit. As another illustration of achange in the plating characteristics .of a chromic acid-- bath, it hasbeen found that an increase in current density at a given temperaturecauses the appearance, hardness and density of the deposited chromium tovary. In other words, the appearance of the deposited chromium may.ljecau'sed to progress from (1) to (2) bright to' States Patent 7tained in equilibrium to provide optimum plating conditions. I

It .will also be recognized that the variables influencing the physicalcharacteristics of the deposited metal must be brought into equilibriumand so maintained without extensive manual supervision if consistent anduniform plating results are to be obtained. By means of the method andapparatus of my invention a heavy, elongate member such as a crankshaftmay be easily raised from the floor, rotatably supported in a chromicacid bath, and as the crankshaft is rotated, the main journals and crankpins thereof are subjected to an eQui-potential anode field whereby auniform deposit of chromium of the desired brightness, hardness anddensity may be deposited thereon.

A major object of my invention is to supply a plating method andapparatus particularly adapted for chromium electroplating, embodying astructure in which a plurality of anode plates are radially disposed andcircumferentially spaced relative to one another to provide anequipotential plating field for a cylindrical surface as it rotatestherethrough.

Another object of my invention is to provide an'electroplating methodand anode structure therefor that is at all times maintained at a fixeddistance from the rotating cylindrical surface being plated, permitsadjustment of the anode current density by the addition or subtractionof anode plates from said supporting structure, by means of which alayer of chromium or other. metal of uniform thickness is deposited oncylindrical surfaces.

' Yet another object of my invention is to provide an electroplatinganode that permits the deposition of a hard, bright chromium plating oncylindrical surfaces without excessive formation of trivalent chromiumoccurring in the plating, bath.

A still further object of my invent-ionis toprovide an electroplatingmethod whereby a hard, bright chromium surface maybe applied to acylindrical surface as a layer of uniform thickness, at a maximum rateof speed without the occurrence of excessive trivalent chromium in'the Afurther object of my invention is to provide an electroplating methodand apparatus therefonwhich are simple in operation, .readily adapted topre-existing electroplating installations, may be operated by relativelyinexperienced personnel, and assures the production of electroplatedcylindrical surfaces of a uniform and quality standard.

I These and other objects and advantages of my lnvention will becomeapparent from the following description of my plating method, and fromthe drawings illustrating an apparatus therefor in which:'

Figure 1 is a cross-sectional view of a plating tank showing myvertically movable apparatus for rotatably supporting a crankshaft asthe cathode mountedtherein, and

with the anodes of my invention operatively associated with the mainjournals and crank" pins for the plating thereof;

Figure 2 is a combined vertical cross-sectional view of the plating tankand an end elevational view of the apparatus utilized in rotatablysupporting a crankshaft;

- Figure .3 is a fragmentary vertical cross-sectional view .of theplating tank and a side elevational view of one of g-my anodesdisposedtherein; 1

. 3 Figure 4 is a fragmentary vertical cross-sectional view of one ofthe rotatable supports for a crankshaft taken on line 4-4 of Figure 2;

Figure 5 is a plan view of one of the anode structures; Figure 6 is avertical cross-sectional view of ananodc structure taken on line 66 ofFigure 5;

Figure 7 is a fragmentary vertical cross-sectional view of an anodestructure taken on line 71 of Figure 6;

Figure 8 is a vertical cross-sectionalview of an anode structure, theplates of which are of an alternate con struction;

Figure 9 isthe same view as that of Figure 7, but showing an anode plateof alternate construction; and,

. Figure 10. is a side elevational view of the lower edge ofan anodeplate, t i

The general arrangement of the apparatus used with myt'method ofelectroplating cylindrical surfaces may best be "seen inFigures l to 6inclusive. An elongate'elec't'ro- 5 plating tank. T is providedthat'hashorizontal and outwardly disposed flanges F formed on the upper edges ofthe sidewalls thereof. The vertically adjustable mechanism M is adaptedto rotatably support a CrankshaftC in a substantiallyhorizontalpositio'n within tank T, with thecrankshaft being rotated by amotor B when so supported, A number of anode structures S rotatablyengage the main journals J and crank pins P of the crankshaft when it'issupported bythe mechanism M; The detailed structure of the preferredform of my anode structure is best illustrated in Figures 5, 6, and 7.

Tank 'T'is 'rectangularly-shaped, and from the bottom 11 thereof endpieces 12, 12 and sidewalls l3, 13"proj'ect upwardly to terminate inflanges F. Each flange F afiixed to side walls 13 and 13' supports twoparallel, laterally spaced bus bars 14, 15 and 14', 15' respectively.Bus bars 14, 14 (see Figure 2) occupy inwardly disposed positions higherin elevation than bus bars 15, 15. The bus bars 14, 15,, 14 and 15 aresupported from flange F'by electrical insulators Bars 14, 14 areconnected to the positive terminal of a source of direct electricalpower (not shown), and bars 15, 15 to the negative terminal of the samesource of power. The bus bars 14, 14"serve to supply electrical energyto the anodes S as will hereinafter be explained in detail, and bars 15,15' supply electrical energy to the crankshaft C, which serves as thecathode. M

H Crankshaft-supporting mechanism M best seen in Figures land 2,includes an elongate, horizontally disposed rigid member 20. Twovertically disposed supports 21 'a'nd 2 l'dep end downwardly from theend portions ,of member 20, :saidfsu'pports each having a combinedbearing and rotary electrical contact 22 and 22' r'esp'ectively,mountedpn thelower ends thereof. Contacts 22 a'n'd 22' arefo'f identicalconstruction. 4 In Figure one of the combined bearing and; rotaryelectrical contacts is shown, and it will seenftofiir clude ahorizontally, disposed cylindrical shell. 23 gidly aflixed to thelower'etid of support'21. The endfport'ioris of shell 23 are tapped,with the outwardly disposed end of said shell having a plug 24 threadedtherein. ,Aibjear- ,inig zs is formed "as a part ot'p1i1g124 situatedt'within the confines of the shell 23. The inwardly 'disposed end ofshell'23 has a threaded sleeve 26 mounted therein The inwardly disposedend portion of a horizontalshaft' is rotatably'supportedin shell 23 bybearing 25 and "sleeve ,fSlie ll IB has Lanjope'ningZS forrn edintheupper porition fj tliereofcommunicating witha vertically positionedtube '2'9. Tube 29 permits the introduction or mercuryY intothenconfines of shell 23, a13cl serves as a housing {or an electrodeBlithat contacts themercury after itfis so int'roduced. Escape ofmercury Y from shell 23 isprevented by means of two annular resilientsealing gaskcts. j

31, and fil'cnc'ircling shaftl'27 which'are compressed be tween bodyshoulders 32, 32' "and the inwardlvdis'pb'sEd endsof bearing 25andsleeve 26 respectively. Electrode 30 has an insulated electricalconductor 33 extending therefrom to a clamp 34 that is removably affixedto one of the bus bars 15. The mercury Y disposed in shell 23 assures agood electrical connection between electrode 30 and shaft 27,irrespective of whether the shaft is stationary or rotating. M

An annular flange 35 is mounted on shaft 27, which flange is a companionto flange 36, which i an integral part of the crankshaft C. The twoflanges 35 and 36 are removably held together by bolts37. The oppositeend portion. of crankshaft C and shaft 27' are removably connected toone another by a collar 38. Shaft 27 has a sprocket 39 mounted thereonthat engages an endless chain belt 40, which belt extends upwardly forengagement with a sprocket 41 mounted on a jack shaft 42. Jack shaft 42is provided with a pulley 43 driven by an endless belt 44 eitendingupwardly'to a drivingpulley .45 on motor E. Motor E and jack shaft 42are supported on a rectangularly-shaped frame '46 rigidly connected tomember 20.. A simila'rlyshaped frame 46' is provided on the opposite endportion of member 20. Frames 46,

rated, electrical conducting tubular members 51, 51.

which may best be seen in Figures 6 and 7. The body of each anode isfabricated from two laterally separated sheets 55, 55' of an invertedU-shape. Sheets 55, '55 are held together as an integral unit by anumber of rigid, transversely disposed rods R that engage the edgeportions thereof. Sheets 55,55 (Figure 6) have matched radially disposedslots 54', 54 respectively, formed on the 'intei-ior'surfaces thereof.Each pair of slots 54, '54" slidably receives an anode plate 56 ofsubstantially rectangular shape in which two angularly disposed cars 57ai e'formedon the outwardly disposed edge'portion'ther'eof. The ears'57, by bolts '58 or other means, are connected ,to a'gi'ou'p ofconcentrically disposed, laterally separated pairs of inverted u shapedelectrical conductors 60,61, and 62. Two pairs of horizontally disposedconductors 63, 64 are. provided that are substantially straight. f Eachof conductors'60, 6 1, 62, 63 and 64 are preferably e le'ctrillyinsulated'from one another to assure that each sa as plate 56 is atthe same electrical potential.

Four rollers 65 (Figures 5 and '6) formed r a'resilient electricalinsulating material are rotatably supported in J "ofj the crankshaftCfto support the anode S thereon.

in Figure 6 itwillbe s'centha't a strip of sheet 'plastic'70orotherfeIecttical insulating material extends around theIoutjeredgefpbrtions of the'sheetsSS, '55,

7 en the anode structure S is supported byrollers '65 above'ac'ylin'drical surface s'uchas amain journal], the inwardly :disposedends of all the anode plates 56, are maintained 'apredetermined[distancefrom the surface being 'plated. Thisp'redetermin'e'd distance Dholds "c'ons'tann -evenas the 'thickness of.thef'depositcd'rnetalfin. creases, for'the referenceplane on whichthe'r'ollers"65 travel is the surface of the deposited film. Thepredetermined distance D (Figure 6) is that space between the exteriorsurface 71 of the layer of deposited metal 72, and the circle 73 shownin phantom line touching the lower edges of anode plates 56. v

Anode plates 56 are equally spaced and radially disposed relative to oneanother. The circle 74 also shown in phantom line in Figure 6, definesthe outer boundary of an equi-potential zone Z wherein each anode plate56 has the same effective area and is at the same potential to cause thedeposition of a layer of chromium on a cylindrical surface. The lowerboundary of the equipotential zone'is substantially defined by thehorizontally disposed phantom line 75. The portions of the anode plates56 and the conductors 60, 61, 62, 63 and 64 outside the equi-potentia'lzone Z may be masked with a coating of electrical insulating material toprevent a distorting effect on the zone thereby.

In the operation of my apparatus and method it is occasionally foundthat the center of the cylindrical surface being plated tends to receivea metal coating thereon at a more rapid rate than the balance ofthesurface. This situation is easily corrected by giving the lower edge 56aof each anode plate 56 a concave curve (see Figure 10). The degree ofconcave curvature must be empirically determined by actual platingtests, and once determined, no further experimental. work will berequired so long as the same physical variables of the plating bathprevail.

In the event it is desired to increase the effective area of the anodeplates 56 within the equipotential zone 2, the plates may be changed tothe alternate corrugated construction shown in Figure 9.' Thiscorrugated anode plate construction is identified in the drawings by thenumeral 56'.

An alternate form of anode structure S is shown in Figure 8, which isessentially identical to my preferred form with the exception that theanode plates 56" thereof are elongate strips bent into the curvedconfigurations shown in .this figure. The ends of the anode plates 56"are all equi-distant from the cylindrical surface 72being plated. Ifdesired, the additional elongate anode plates 56" shown in phantom linemay be added to completely encircle the cylindrical surface Theapplication of my invention is extremely simple. Mechanism M, inasmuchas it is supported from chain falls, may be easily lowered into orraised from the electroplating tank T. This particular mode ofsupporting mechanism M is of a distinct advantage, as it permits freeuse thereof with any one of a number of electroplating tanks. Thestructure of mechanism M provides a further advantage in that thesupports 21, 21' and the frames 46, 46' associated therewith may belongitudinally adjusted on member 20 by use of suitable locking means,not shown. Thus by longitudinal adjustment of supports 21 and 21', themechanism may be adapted to rotatably support crankshafts C of variouslengths.

After a crankshaft C is rotatably supported by the mechanism M, theanode structures S are mounted on the mechanism in the positions shownin Figure 1. Motor E is then actuated, causing crankshaft C to rotate ata uniform rate of speed. The electrical circuit used in the platingoperation is completed when electrical current is supplied to thecrankshaft C serving as the cathode through the rotary mercury contact(Figure 4). As the crankshaft C is rotated, those anodes S resting onthe crank pins P will reciprocate up and down as they follow thecircular path of the pins, with the tubular members 51, 51 beingslidably guided by the eyes 50. Those anodes S resting on the mainjournals I will, of course, not be subjected to reciprocatory motion.

As a cylindrical surface 71 rotates, it continues to pass through theequi-potential zone Z (Figure 6) wherein it is subjected to a continuousand uniform electro-chemical any desired number of anode plates, aswellas-any desired size thereof in order to establish the zone Z at theproper electrical potential and secure optimum plating results.Furthermore, the anode plates 56, 56', and 56" may be easily removedfrom or inserted between plates 52 whenever necessary.

It has been found that my plating apparatus and method will operate in aconsistent and uniform manner after extensive use and provide results ofa much higher quality than heretofore available. I

Although my invention is fully capable of achieving the results andproviding the advantages hereinbefore mentioned, it is to be understoodthat it is merely the presently preferred embodiment thereof and that Ido not mean to be limited to the details of construction or the methodsteps above described other than as defined in the appended claims.

I claim:

1. An anode structure for chromium electroplating a cylindrical cathodesurface of a crank pin as it rotates in a circular path in a verticalplane, which includes: two laterally spaced inverted substantiallyU-shaped sheets fabricated from an electrical insulating acid-resistantmaterial, which sheets are formed. with horizontal lower edges on whichsaid anode may be supported in an upright position when not in use;means for maintaining said sheets including the lower portions thereofin a predetermined laterally spaced relationship; a plurality ofcircumferentially spaced, transversely disposed shafts extending betweensaid sheets; a plurality of rollers mounted on said shafts, said rollersadapted to rotatably-contact said cylindrical surface and maintain saidsheets at a fixed predetermined distance therefrom; a plurality of anodeplates; electrical insulating means separating said plates; means forremovably supporting said plates in fixed, circumferentially spaced,radially disposed positions between said side walls in sufiicientquantity as to provide a desired area ratio between said anode and saidsurface; and electrical power supply means that supply substantially thesame potential for each of said anode plates.

2. An anode structure capable of supporting a plurality of anode platesto obtain a desired cathode current density in the chromiumelectroplating of a cylindrical surface as it rotates in a circular pathin a vertical plane, which includes: two laterally separated sheetshaving a substantially inverted U-shape that may partially encircle saidsurface, said sheets being formed of a rigid, acidresistant, electricalinsulating material having a plurality of complementary slots formed inthe interior surfaces thereof, which slots are in circumferentiallyspaced and radially disposed relationship, the flat lower edges of whichsheets are normal to the sides thereof; means for holding said sheets ina fixed laterally spaced relationship with one another; a plurality ofanode plates formed with two parallel longitudinally extending edges,said pl ates being of such width as to be slidably and removablysupported in two of said complementary slots, the number of said platesbeing that required to provide the desired cathode current density when.said anode plates are supplied with a predetermined quantity ofelectrical power; a plurality of electrical conductors that supply saidelectrical power to said plates when supported between said sheets;means to support said sheets on the upper portion of said cathodesurface as it rotates, and maintain them at a fixed distance therefrom;and an elongate tubular member extending upwardly from said sheets andrigidly connected thereto, said member serving as a housing throughwhich insulated electrical conducting leads may be extended to saidconductors, which tubular member acts as a guide in regulating thepositions of said sheets during rotation of said cylindrical surface,said member also serving as a handle for moving said anode structurewhen placing said sheets upon the supporting surface of said structurein an upright position to rest on said lower flat edges thereof.

sa a-15a- 3. An anode" structure for chromium'electroplatin'g a rotatingcylindrical surface; as it rotates about a subst'antially horizontal:axi'sgfata desiredcathode ctir r'eiit-- density, which includes: twolaterally separated sh'eet's having-a substantially inverted u-shapethat'may partially encircle said surface, which sheets are formedof anacid resistant electrical insulating material: havingfiatdower edges onwhich said-anode rnay be supportedinfian upright position when notinuse; means for"rnaintaining saidsheets' including the lower portionsthereof in afi xe'd laterally spaced relationship; means for removablysupporting a plunality of-spaced -radially disposedano'de plates betweensaid'sheets; a plurality of anode plates held in- -sai'd supportingmeans, with the n'um'b'erof *said plates =so held being that required tosupply said eurrentdensity; roller means rotatably supportedbetween saidsheets "that mov ably engage said surface being platedtosupport saidanode structure thereon and maintain the inwardly disposed ends of saidanode platesat a predetermined distance therefrom during theplating'operation; and means to -supply electrical energy to saidanodeplates.

"4. An anode structure 'for chromium electroplating a cylindricalsurface as it revolves in a circular path in a vertical plane at adesired cathode current density, which includes: two laterally sepanatedsheets having a substantially inverted U-shape that may partiallyencircle said surface, which sheets are formedof an acid-resistant,electrical insulating material; means for maintaining said sheets in afixed laterally spaced relationship; meansfor removably supporting aplurality of spaced, radially' di'sposed anodeplates between saidsheets; a' plurality of anode plates held in said supporting means;means mounted on said sheets that movably engages'aid cathode surfaceto' support said anode structure therefrom and maintain the inner endsof said anode-plates "a't'a prede termined distance from thecathode-plated surface; "and means to-supply electrical energy to saidanode plates.

5. IAn-anodc structure for chromium clectro-plating a circumferentiallyextending section of specific width on a cylindrical cathode surface asit rotates about a substantially horizontal axis in a plating bath,including: a plurality of rigid anode plates of substantially the widthof said'section, with the surface area of said plates being greater thanthat of said cathode-surface so that no substantial quantity-pf tritialent' chromium forrns in {said bath 'd'uringth'c platingfoperatiouywhich plates are circumferentiallyspac'edfrom one another'andqhave portions thereof adjacent said cathode surface which aresubstantially radially disposed relative to said-cathode surface; rigidelcctribal conducting rne'ansaHiXed' to said plates, whichfmean'smaintains said platesin'saidspaced; relationship; an assembly comprisingvertically disposed spaced end sheets formed of an "electricalinsulating materiahpositioned 'adjacentthe ends 'of said plates, 'saidsheets having-rccesses'formed therein that partially encircle saidsurface, with, the'edges' of saidshe'ets, defining saidrecesses;locatedcloselyadjacent to said' cathode.surfa'cesothat' only-saidsection of' sp'ecific width is plated; andmeansforsnpportipgfsaid-plates, conducting means andend sheets at afixed distance rmm'sard cathodelsurface as said surface rotates. v

6. An anode structureas defined incl'aim 5 in which at least a'p'ortio'nofsaid anode plates are other than flat-in shape so that the surface ofsaid plates exposed tosaidbath is increased.

7. An anode structure as defined in claim 5 in'which at least a portionof said anode plates are so formed as to define a corrugated transversecross section to increase the surface area of said plates exposed tosaid bath.

'8. An anode sttfucturefatldefined in claim 5 in which the ends of saidano'de 'plates adjacent said cathode surface are concave so that achromium layer of uniform thickness is deposited on said cathodesurface.

9. An anode structure vasdefirmd in claim 5 in which saidsupporting'rneansarerollers that rest on said cathode surface.

References Cited inthefile of this patent. UNITED sr rEs PATENTS 6804ll8 Cowper-(Boles Aug. :13, 1901 2,457,510 Van Ornum Dec. 28,-.1948;2',-473, 290 Millard June 14, 1949 2,530,677 lBurkenkotter Nov. 21,4950,

FOREIGN-PATENTS 18,643 Great Britain aof 1899

1. AN ANODE STRUCTURE FOR CHRONIUM ELECTROPLATING A CYLINDRICAL CATHODESURFACE OF A CRANK PIN AS IT ROTATES IN A CIRCULAR PATH IN A VERTICALPLANE, WHICH INCLUDES: TWO LATERALLY SPACED INVERTED SUBSTANTIALLYU-SHAPED SHEETS FABRICATED FROM AN ELECTRICAL INSULATING ACID-RESISTANTMATERIAL, WHICH SHEETS ARE FORMED WITH HORIZONTAL LOWER EDGES ON WHICHSAID ANODE MAY BE SUPPORTED IN AN UPRIGHT POSITION WHEN NOT IN USE;MEANS FOR MAINTAINING SAID SHEETS INCLUDING THE LOWER PORTIONS THEREOFIN A PREDETERMINED LATERALLY SPACED RELATIONSHIP; A PLURALITY OFCIRCUMFERENTIALLY SPACED, TRANSVERSELY DISPOSED SHAFTS EXTENDING BETWEENSAID SHEETS; A PLURALITY OF ROLLERS MOUNTED ON SAID SHAFTS, SAID ROLLERSADAPTED TO ROTATABLY CONTACT SAID CYLINDRICAL SURFACE AND MAINTAIN SAIDSHEETS AT A FIXED PREDETERMINED DISTANCE THEREFROM; A PLURALITY OF ANODEPLATES; ELECTRICAL INSULATING MEANS SEPARATING SAID PLATES; MEANS FORREMOVABLY SUPPORTING SAID PLATES IN FIXED, CIRCUMFERENTIALLY SPACED,RADIALLY DISPOSED POSITIONS BETWEEN SAID SIDE WALLS IN SUFFICIENTQUANTITY AS TO PROVIDE A DESIRED AREA RATIO BETWEEN SAID ANODE AND SAUDSURFACE; AND ELECTRICAL POWER SUPPLY MEANS THAT SUPPLY SUBSTANTIALLY THESAME POTENTIAL FOR EACH OF SAID ANODE PLATES.